Chaired by:
Igor Dawid, NICHD

Balcony B, Natcher Conference Center

During development, the formation of different cell types, tissues, and organs is controlled by two major processes: cell autonomous events in which fate is controlled by intrinsic determinants inherited by a cell, and non-cell autonomous events that depend on cellular interactions. Cell interactions through a variety of signaling mechanisms are essential in all developmental processes, and consequently elucidation of these mechanisms is a major concern of research in developmental biology. Comparatively few families of signaling molecules dominate the regulation of embryogenesis in metazoan animals; yet, the combination of cues leads to a large variety of inputs that are possible. Furthermore, the same signaling molecule may be used repeatedly during development, yielding multiple results dependent on context. The response of a cell to a signal depends on the status of the cell, a property called competence that is often the consequence of earlier signals received by the cell or its precursors. In this symposium, four examples of developmental processes in vertebrate embryos that depend on intercellular signals will be discussed, highlighting functions of members of two major classes of signaling molecules. The TGF-beta class of factors includes the important subclasses of nodal and bone morphogenetic proteins (BMPs). Nodal is known to be essential for gastrulation in the mouse, but has additional major functions in subsequent development, notably in the establishment of left-right asymmetry. Aspects of nodal function will be discussed by Dr. Kuehn. The role of the other subclass, the BMPs, in early mouse development is the subject of Dr. Mishina's lecture which indicates examples of left isomerism and situs inversus in Alk2 chimeras. The talk by Dr. Yamaguchi will discuss the role of Wnt factors in the very early embryo where they are known to be essential in the initial specification of the major body axis. Illustrating the principles that the same factors are used repeatedly at different stages of development and that combinatorial signaling inputs are often essential, Tom Sargent will discuss neural crest formation where both the BMP and Wnt pathways play an essential role. Thus, this symposium will provide some examples of developmental mechanisms that depend on signaling factors and cellular reponses to their action.

Program

Control of Neural Crest Development in Xenopus
Thomas Sargent, NICHD

Wnt Signaling and Axis Formation
Terry Yamaguchi, NCI

Functional Analyses of Bone Morphogenetic Proteins during Pattern Formation and Mesoderm Specification in Mouse Embryos
Yuji Mishina, NIEHS

Conditional Approaches to Study Nodal Signaling during Mouse Development
Michael Kuehn, NCI